Optical fiber cables have been a very popular medium for communications and data transmission due to their high speeds and suitability over long distances. The transmission medium of optical fiber cables consist of thin optical fibers protected from external forces and elements by precisely designed and manufactured cable structures. One common cable structure used is the loose-tube cable. The loose-tube cable contains one or more buffer tubes arranged around a central strength member. The buffer tubes loosely encase one or more optical fibers, either in bundles or ribbons, thereby providing sufficient room for the fiber(s) to move within the buffer tube in response to applied stresses. The space inside the buffer tubes between the fibers and the buffer tube is filled with a waterblocking filling material to protect the fibers from water penetration. The buffer tubes can then be wrapped with binders, tapes, or yarns to provide additional strength and protection. Finally, the cable assembly is encased within a cable jacket to provide mechanical strength and protection from the environment.
The loose-tube cable design permits easy drop-off of groups of fibers at intermediate points without interfering with other buffer tubes being routed to other locations. Since not all fibers, or groups of fibers, will always be routed to the same location or terminal application, it is necessary to be able to identify and distinguish among the various groups of fibers and among individual fibers. Because of the vast quantity of optical fibers that may be contained in an optical fiber cable, a color coding scheme is most commonly used to identify the buffer tubes and the individual optical fibers therein. This color-coding scheme generally consists of color-coding the buffer tubes and individual fibers. Usually the color-coding complies with EIA/TIA-598 color specifications.
Traditionally, individually colored buffer tubes are produced by adding and mixing a colorant in an extruder or other high pressure mixing device prior to extrusion of each individual tube. Coloring buffer tubes requires mixing the buffer tube material with a color concentrate, or colorant, in an extruder or other high temperature and high pressure mixing device prior to extrusion each time a different tube color is desired. This results in substantial delays and down times just to change the tube color. Tube colorants can also be quite expensive. These colorants typically contain a pigment, dye or other coloring concentrate carried in a base resin. The buffer tube material and the base resin for the color concentrate should be the same type of material because of material incompatibility. Since the buffer tube material generally comprises polybutylene terephthalate (PBT), polyester elastomer, nylon, fluoropolymer, acetal resin or polycarbonate, the colorants that can be used become quite expensive.
Finally, color-coding buffer tubes is not suitable for cables having a high number of buffer tubes. The buffer tubes of cables having more than twelve buffer tubes are marked by the placement of rings, bands, stripes or identification threads/tapes around or in the buffer tubes. These cables are expensive to produce, and require cutting away substantial portions of the outer jacket to locate any such marking.